The invention relates to a measuring and control device for guiding a steel belt along the longitudinal axis of a continuously operating press for the production of particle boards, fiber boards or similar wood boards and plastic boards.
In continuously operating presses of this type, as the presses are lengthened to attain greater output capacities, the adjustment of the steel belt necessary for straight-line running about the longitudinal axis cannot be accomplished too easily. The limit lies roughly at a length of 28 meters for a continuously operating press. As the lengths increase towards 40 meters and more, for example,
a) slight irregularities in the lubrication of the steel belts and rolling rods or PA1 b) uneven bulk-density distribution
have a disruptive effect upon on-line adjustment. Therefore, it is not always possible to redirect the steel belts into the middle by angular adjustment of the driving drum and reversing drum axes as according to German Patent Specification 26 43 346.
In the press/heating platen region, particularly in the first third of the high-pressure area, the steel belts are tightly clamped as in a vice. As a result, whenever the drum axes are adjusted by means of the adjustment path, an elongation partially greater than in the clamped region is obtained in the entry region because the steel belt is not clamped here. The same applies to the exit strand. As a result, in the high-pressure region of the presses which are becoming longer the elongation in the clamped zone is small relative to the entry and exit sections. Therefore, in order to prevent one-sided overexpansion of the steel belts as the course of the steel belt is adjusted, the continuously operating press has to be halted and all the inconveniences and disadvantages associated with halting of the press have to be endured.
In order to overcome and resolve these difficulties, German Offenlegungsschrift 40 17 791 discloses a process by which the course of the steel belt relative to the longitudinal center axis can be adjusted during running of the continuously operating press without any one-sided overexpansion of the steel belt, and a device in which this process can be implemented.
According to the solution discovered, the axial adjustment is carried out on one of the longitudinal sides, by an angle beta, on the reversing drum and/or driving drum axes, at the start of an adjustment of the press ram; the press ram is transported by the short-stroke pressure cylinder in the high-pressure region out of its horizontal position into an oblique position such that, on the left or right in the direction of entry, a pressure profile or path profile is set. This process and device have become established for adjusting the course of the steel belt for large press lengths.
The above measuring and control devices are unable however to cope with temperature differences, for example, temperature differences resulting from thermodynamic air movements occurring within a factory hangar on the left or right of the longitudinal sides of the press, which give rise to greater differences in linear expansion. Where a temperature difference of about 10.degree. C. exists, for example, from one longitudinal side to the other, a difference in length of approximately 6 millimeters from one longitudinal side to the other is obtained for a free expansion length L of about 50 meters.